ResultMessage is being sent while background agent is still working and turn is finished

I'm using the SDK in streaming mode (calling `client.query()` and `client.receive_response()`), somewhere between `0.2.110` and `0.2.121`, the behavior of the Agent SDK broke for me.

Before, it would only send the `ResultMessage` at the complete end of the turn. However, I now notice behavior where a background agent is still running, but the `ResultMessage` has already been delivered and the `client.query()` already returned, this causes the Agent SDK to miss messages when the background agent finishes.